I have "hatched" 3 bamboos in the past, and I think it's best to let them do it on their own also. Just keep a close eye on him. I have seen one egg case that was cut open on top so there was kind of a semicircular flap, but when the owner saw the shark was actually just fine, he left it be and it stayed in the case until it was ready. He was lucky he didn't knick the shark. It irritates me when pet stores promote the "just cut it out" idea, most first time owners don't know what to expect and get worried when it takes a while. I had one take 3 months, just depends on how developed they are when purchased.
In the few hatchings I've seen, the shark always pushed through the end of the case, usually at night. Except in one case where I was holding a mature egg up (still underwater) to see how he was doing and the shark just jumped out of the end of the case with it in my hands. I think we were both suprised.
Also, make sure you have a lid on that tank.